The invention relates to a method for determining the pressure comfort of seat cushions.
In the development of seats, especially vehicle seats, a question of good pressure comfort arises because the occupants, and especially the driver, sometimes have to remain seated on vehicle seats for many hours with only limited movement. In this regard, questions of optimum seat pressure distribution play a role. The behavior of a seat in this regard is determined by a number of factors, for example the design, structure, and finishing of the multi-layer combination of the covering material and the material, type, and structure of the seat foundation and the like. If the sitting pressure of a seat cushion is unfavorable when an individual sits on it, it will be perceived as unpleasant and uncomfortable for prolonged sitting.
In the course of seat development, various seat and cushion designs are prepared as trial samples and these must be compared with one another in an objective and reproducible fashion regarding various testing and evaluation criteria, especially as regards pressure comfort, in order to be able to pick the best trial sample in this way. Not only new trial samples from actual seat development but also various test seats from other sources, for example seats of earlier seat generations, used seats, or seats from outside development or manufacturing facilities, are compared with one another.
In the past, comfort-relevant seat testing could only be performed by test subjects. This of course produces only subjective test results that depend on how the individual tested was feeling that day, in other words results that are inaccurate and nonreproducible. Such tests are also costly in terms of time and personnel because the test must be performed in the vehicle and by several test subjects in order to yield results that show less scatter. The installation of a seat to be tested in a vehicle is also time-consuming, especially when comparison-testing objects from outside manufacturers.
The goal of the invention is to provide a method that offers a quantitative, realistic, and reproducible statement about the pressure comfort of test seats when testing seats for pressure comfort.
This goal is achieved according to the invention by a method for determining the pressure comfort of a seat cushion. According to this method, during realistic mechanical loading of the seat with the seat cushion to be tested, the sitting pressure distribution on the surface of the seat is measured with a suitable known measuring mat and the signals from the individual pressure sensors in the measuring mat are evaluated. For this purpose, the measurement signals from suitably anthropomorphically determined loading areas with different pressure sensitivity thresholds are combined in groups and evaluated separately for the individual areas. In each area, the pressure measurement values are evaluated in accordance with the magnitude of the determined pressure, i.e. multiplied by a factor. The greater the pressure in a certain sensor field differs from the pressure sensitivity threshold, the higher this measured value is rated and the higher the corresponding quality factor, with a pressure-dependent progressively increasing quality factor being used in this case. The pressure sensitivity threshold (p.sub.0) of the respective area is assigned a value of 1 as a quality factor. Depending on the difference between the individual measured pressure value and the pressure sensitivity threshold, the quality factor increases progressively with an increasing difference. By means of the multiplicative evaluation of the pressure distribution function, a product function is obtained for each area of the seat and is then integrated. The sum of the integral values of the product functions obtained is output as the rating number for the pressure comfort of the cushion.
The sitting surface of the seat cushion to be tested can be stressed by a seated test subject or, preferably, by means of an anthropomorphically designed seat testing punch. The comfort test can be conducted with persons of different sizes or with seat testing punches of different sizes (5%, 50%, and 95% percentiles), and an average or sum of all the results can be used as a rating number for pressure comfort.
In conjunction with optimum sitting pressure distribution, it can be said in general that body weight when sitting should optimally be supported by the buttocks and therefore primarily by the two so-called ischial humps. The sitting pressure distribution should therefore have pronounced maxima in the vicinity of the two ischial humps, said maxima making a gentle transition to a lower pressure level in the surrounding area, while in the vicinity of the thighs the sitting pressure should be as flat as possible and taper to zero at the edge of the cushion that faces the backs of the knees.
The measurement principle is based on human perception of the sitting pressure. The receptors in humans that feel contact pressure are distributed over the entire body surface. The sensitivity of the receptors differs in various skin areas, however. Sensitivity to pressure depends on the following: (1) the respective sensitivity of the skin area to which the pressure is being applied; (2) the size of the area exposed to the pressure, in other words the number of receptors that are impacted above the pressure sensitivity threshold; (3) the magnitude of the stimulus; (4) the fact that subjective pressure sensitivity increases exponentially with increasing application of pressure; and (5) the duration of the stimulating effect.
Practical experience with the measurement method according to the invention and a comparison of the measured pressure comfort numbers for various seats with subjective statements from test subjects who tested the seats confirm that the measurement method offers quantitatively reproducible and especially representative information about the pressure comfort of seats.
The following advantages can be achieved by the invention:
(1) the tests proceed under exactly defined measurement conditions;
(2) the anatomy and anthropomorphy of human beings as well as the subjective sensitivity of the test subjects are the basis of the measurement method and signal evaluation;
(3) measurement results are obtained that are reproducible and representative of pressure comfort, in other words they are objective;
(4) series measurements with anthropomorphically designed seat testing punches are quite possible, especially if the optimum quality number range has first been determined by statistical tests on human subjects;
(5) the measurement results from different seats, new developments from one's own development program, or seats from other manufacturers can be assigned to a uniform measurement scale and compared with one another as a result without difficulty;
(6) differences and special features of pressure distribution that cannot be detected by simply looking at a pressure distribution diagram are clearly shown by the measurable pressure comfort number and therefore can be followed systematically for the first time;
(7) as a result of the invention, seat development can proceed more clearly for optimum seat pressure comfort and can be considerably speeded up;
(8) since the measurement method proceeds in all phases under defined conditions and leads to a reproducible, representative, and numerical measurement result, the measurement method can be standardized, which would considerably facilitate contact between seat suppliers and automobile developers.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.